This invention relates generally to methods and apparatus for measuring the muzzle velocity of a projectile ejected from a gun barrel, and, more particularly, to methods and apparatus of this kind that measure velocity using Doppler radar.
Apparatus of this particular kind are frequently called muzzle velocity chronographs. They include a radar device mounted on the gun barrel for directing a radar signal at the ejected projectile and correlating the radar signal with a reflected return signal, to produce a conventional Doppler signal. Each cycle of the Doppler signal represents movement of the projectile by a distance equal to one-half the wavelength of the radar signal. The typical muzzle velocity chronograph counts the number of cycles occurring in the Doppler signal per unit time, to determine the projectile's velocity. This process is repeated incrementally, to produce a velocity profile, from which the projectile's initial, muzzle velocity can be determined.
Chronographs of the kind described above, which utilize time domain processing, are usually effective in measuring a projectile's muzzle velocity. However, such chronographs have not proven to be entirely effective in situations where the return signal from the projectile is relatively weak or where substantial interference is present. This occurs, for example, when certain base-bleed ammunition is used, which produces fragments that are significantly larger than the projectile of interest.
It should therefore be appreciated that there is a need for an improved muzzle velocity chronograph that can effectively measure a projectile's muzzle velocity even when the projectile is relatively small and when the projectile is moving in the same direction as larger radar-reflecting fragments. The present invention fulfills this need.